MTD: NAND: Fix bad-block detection for 8-bit NAND

Hi Thomas,

I found the following block in our 128MiB NAND flash:

hexdump vic.img.460
0000000 0000 0000 0000 0000 0000 0000 0000 0000
*
0000800 00ff 0000 0000 0000 0000 0000 0000 0000
0000810 0000 0000 0000 0000 0000 0000 0000 0000
*
0001040 00ff 0000 0000 0000 0000 0000 0000 0000
0001050 0000 0000 0000 0000 0000 0000 0000 0000
*
0021000

According to the specification this is a good block, because the bytes in the 1st two OOB areas at offset 0 are 0xff. Nevertheless it was detected bad because:

static struct nand_bbt_descr largepage_memorybased = {
	.options = 0,
	.offs = 0,
	.len = 2,                    /* <<<< bytes to check!!! */
	.pattern = scan_ff_pattern
};

used a len of 2 instead of 1, which I consider to be correct. Here a potential fix for the problem. Please have a look if it matches your understanding of the specification.

Signed-off-by Frank Haverkamp <[email protected]>

---
 drivers/mtd/nand/nand_bbt.c |   20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

drivers/mtd/nand/nand_bbt.c +17 -3

@@ -1081,7 +1081,14 @@ static struct nand_bbt_descr smallpage_m
 	.pattern = scan_ff_pattern
 };
 
-static struct nand_bbt_descr largepage_memorybased = {
+static struct nand_bbt_descr largepage_memorybased_8bit = {
+	.options = 0,
+	.offs = 0,
+	.len = 1,
+	.pattern = scan_ff_pattern
+};
+
+static struct nand_bbt_descr largepage_memorybased_16bit = {
 	.options = 0,
 	.offs = 0,
 	.len = 2,

@@ -1179,8 +1186,15 @@ int nand_default_bbt(struct mtd_info *mt
 		this->bbt_td = NULL;
 		this->bbt_md = NULL;
 		if (!this->badblock_pattern) {
-			this->badblock_pattern = (mtd->writesize > 512) ?
-			    &largepage_memorybased : &smallpage_memorybased;
+			if (mtd->writesize > 512) {
+				if (this->options & NAND_BUSWIDTH_16)
+					this->badblock_pattern =
+						&largepage_memorybased_16bit;
+				else
+					this->badblock_pattern =
+					       &largepage_memorybased_8bit;
+			} else
+				this->badblock_pattern = &smallpage_memorybased;
 		}
 	}
 	return nand_scan_bbt(mtd, this->badblock_pattern);